1. Field of the Invention
The present invention relates to a steam reforming system utilizing flue gases of a gas turbine, and more particularly to a steam reforming system equipped with a pre-reformer, which is used for a plant producing hydrogen, ammonia, methanol, etc. by using hydrocarbons with carbon numbers of C2 or more as feedstocks.
2. Description of the Related Art
A reformer is employed in production processes for hydrogen, ammonia, methanol, etc. to produce, from hydrocarbons supplied as feedstocks, synthesis gases that serve in turn as feedstocks for producing those products. The hydrocarbons supplied as feedstocks are pressurized to a level of required pressure, and then subjected to preheating and desulfurization. After being mixed with steam, the feedstocks are heated to about 500° C. through heat exchange with flue gases leaving the reformer, and are introduced to a heated pipe of the reformer which is filled with a steam reforming catalyst. The introduced feedstocks are exposed to the heat of combustion gases of the reformer and are converted to the synthetic gases. For example, when the feedstocks are reformed for conversion to the synthetic gases under pressurization at a pressure of about 20 atmospheres, the reforming temperature is not lower than 800° C. and therefore a large amount of fuel used for the heating is required.
As methods for saving fuel used for the heating, Patent Reference 1; JP,A 06-207531, for example, proposes a system (hereinafter referred to as a “steam reforming system utilizing flue gases of a gas turbine”) in which a gas turbine is additionally installed in combination with a reformer to produce electric power, and high-temperature flue gases of the gas turbine are introduced as combustion air to the reformer. Another proposal is a system (hereinafter referred to as a “pre-reforming system”) in which the fuel consumption in the reformer is reduced by installing a pre-reformer upstream of the reformer to convert heavy hydrocarbons in feedstocks to methane in advance, thereby increasing the temperature at a reformer inlet, which has hitherto been limited to a level not higher than about 500° C. for the purpose of preventing a trouble of carbon formation due to thermal cracking of the feedstocks at the reformer inlet, up to a level of 550-600° C. through heat exchange with flue gases of the reformer.
Also, in the steam reforming system of JP,A 06-207531, a part of the high-temperature flue gases of the additionally-installed gas turbine is directly introduced to a heating furnace via a flue gas channel, and a regular or emergency blower is installed to be ready for unexpected stop of the gas turbine so that air exiting the blower can be introduced to some midpoint of the exhaust gas channel.
Further, in the known pre-reforming system, the feedstocks must be desulfurized before being introduced to the pre-reformer, and a preheater furnace is installed to preheat the feedstocks up to the temperature required for desulfurization. The temperature of the feedstocks must be further increased to perform a pre-reforming stage, and the flue gases of the reformer are employed as a heat source for that purpose. More specifically, a heating coil is inserted in a reformer's convection section to heat the feedstocks up to the temperature required for the pre-reforming stage, and the preheated feedstocks are introduced to the pre-reformer.